- •24.3 HYDRAULICS
- •24.4 OTHER SYSTEMS
- •24.5 SUMMARY
- •24.6 PRACTICE PROBLEMS
- •24.7 PRACTICE PROBLEM SOLUTIONS
- •24.8 ASSIGNMENT PROBLEMS
- •25. CONTINUOUS CONTROL
- •25.1 INTRODUCTION
- •25.2 CONTROL OF LOGICAL ACTUATOR SYSTEMS
- •25.3 CONTROL OF CONTINUOUS ACTUATOR SYSTEMS
- •25.3.1 Block Diagrams
- •25.3.2 Feedback Control Systems
- •25.3.3 Proportional Controllers
- •25.3.4 PID Control Systems
- •25.4 DESIGN CASES
- •25.4.1 Oven Temperature Control
- •25.4.2 Water Tank Level Control
- •25.5 SUMMARY
- •25.6 PRACTICE PROBLEMS
- •25.7 PRACTICE PROBLEM SOLUTIONS
- •25.8 ASSIGNMENT PROBLEMS
- •26. FUZZY LOGIC
- •26.1 INTRODUCTION
- •26.2 COMMERCIAL CONTROLLERS
- •26.3 REFERENCES
- •26.4 SUMMARY
- •26.5 PRACTICE PROBLEMS
- •26.6 PRACTICE PROBLEM SOLUTIONS
- •26.7 ASSIGNMENT PROBLEMS
- •27. SERIAL COMMUNICATION
- •27.1 INTRODUCTION
- •27.2 SERIAL COMMUNICATIONS
- •27.2.1.1 - ASCII Functions
- •27.3 PARALLEL COMMUNICATIONS
- •27.4 DESIGN CASES
- •27.4.1 PLC Interface To a Robot
- •27.5 SUMMARY
- •27.6 PRACTICE PROBLEMS
- •27.7 PRACTICE PROBLEM SOLUTIONS
- •27.8 ASSIGNMENT PROBLEMS
- •28. NETWORKING
- •28.1 INTRODUCTION
- •28.1.1 Topology
- •28.1.2 OSI Network Model
- •28.1.3 Networking Hardware
- •28.1.4 Control Network Issues
- •28.2 NETWORK STANDARDS
- •28.2.1 Devicenet
- •28.2.2 CANbus
- •28.2.3 Controlnet
- •28.2.4 Ethernet
- •28.2.5 Profibus
- •28.2.6 Sercos
- •28.3 PROPRIETARY NETWORKS
- •28.3.1 Data Highway
- •28.4 NETWORK COMPARISONS
- •28.5 DESIGN CASES
- •28.5.1 Devicenet
- •28.6 SUMMARY
- •28.7 PRACTICE PROBLEMS
- •28.8 PRACTICE PROBLEM SOLUTIONS
- •28.9 ASSIGNMENT PROBLEMS
- •29. INTERNET
- •29.1 INTRODUCTION
- •29.1.1 Computer Addresses
- •29.1.2 Phone Lines
- •29.1.3 Mail Transfer Protocols
- •29.1.4 FTP - File Transfer Protocol
- •29.1.5 HTTP - Hypertext Transfer Protocol
- •29.1.6 Novell
- •29.1.7 Security
- •29.1.7.1 - Firewall
- •29.1.7.2 - IP Masquerading
- •29.1.8 HTML - Hyper Text Markup Language
- •29.1.9 URLs
- •29.1.10 Encryption
- •29.1.11 Compression
- •29.1.12 Clients and Servers
- •29.1.13 Java
- •29.1.14 Javascript
- •29.1.16 ActiveX
- •29.1.17 Graphics
- •29.2 DESIGN CASES
- •29.2.1 Remote Monitoring System
- •29.3 SUMMARY
- •29.4 PRACTICE PROBLEMS
- •29.5 PRACTICE PROBLEM SOLUTIONS
- •29.6 ASSIGNMENT PROBLEMS
- •30. HUMAN MACHINE INTERFACES (HMI)
- •30.1 INTRODUCTION
- •30.2 HMI/MMI DESIGN
- •30.3 DESIGN CASES
- •30.4 SUMMARY
- •30.5 PRACTICE PROBLEMS
- •30.6 PRACTICE PROBLEM SOLUTIONS
- •30.7 ASSIGNMENT PROBLEMS
- •31. ELECTRICAL DESIGN AND CONSTRUCTION
- •31.1 INTRODUCTION
- •31.2 ELECTRICAL WIRING DIAGRAMS
- •31.2.1 Selecting Voltages
- •31.2.2 Grounding
- •31.2.3 Wiring
- •31.2.4 Suppressors
- •31.2.5 PLC Enclosures
- •31.2.6 Wire and Cable Grouping
- •31.3 FAIL-SAFE DESIGN
- •31.4 SAFETY RULES SUMMARY
- •31.5 REFERENCES
- •31.6 SUMMARY
- •31.7 PRACTICE PROBLEMS
- •31.8 PRACTICE PROBLEM SOLUTIONS
- •31.9 ASSIGNMENT PROBLEMS
- •32. SOFTWARE ENGINEERING
- •32.1 INTRODUCTION
- •32.1.1 Fail Safe Design
- •32.2 DEBUGGING
- •32.2.1 Troubleshooting
- •32.2.2 Forcing
- •32.3 PROCESS MODELLING
- •32.4 PROGRAMMING FOR LARGE SYSTEMS
- •32.4.1 Developing a Program Structure
- •32.4.2 Program Verification and Simulation
- •32.5 DOCUMENTATION
- •32.6 COMMISIONING
- •32.7 REFERENCES
- •32.8 SUMMARY
- •32.9 PRACTICE PROBLEMS
- •32.10 PRACTICE PROBLEM SOLUTIONS
- •32.11 ASSIGNMENT PROBLEMS
- •33. SELECTING A PLC
- •33.1 INTRODUCTION
- •33.2 SPECIAL I/O MODULES
- •33.3 SUMMARY
- •33.4 PRACTICE PROBLEMS
- •33.5 PRACTICE PROBLEM SOLUTIONS
- •33.6 ASSIGNMENT PROBLEMS
- •34. FUNCTION REFERENCE
- •34.1 FUNCTION DESCRIPTIONS
- •34.1.1 General Functions
- •34.1.2 Program Control
- •34.1.3 Timers and Counters
- •34.1.4 Compare
- •34.1.5 Calculation and Conversion
- •34.1.6 Logical
- •34.1.7 Move
- •34.1.8 File
- •34.1.10 Program Control
- •34.1.11 Advanced Input/Output
- •34.1.12 String
- •34.2 DATA TYPES
plc software - 32.3
32.2.1 Troubleshooting
After a system is in operation it will eventually fail. When a failure occurs it is important to be able to identify and solve problems quickly. The following list of steps will help track down errors in a PLC system.
1.Look at the process and see if it is in a normal state. i.e. no jammed actuators, broken parts, etc. If there are visible problems, fix them and restart the process.
2.Look at the PLC to see which error lights are on. Each PLC vendor will provide documents that indicate which problems correspond to the error lights. Common error lights are given below. If any off the warning lights are on, look for
electrical supply problems to the PLC. HALT - something has stopped the CPU
RUN - the PLC thinks it is OK (and probably is) ERROR - a physical problem has occurred with the PLC
3.Check indicator lights on I/O cards, see if they match the system. i.e., look at sensors that are on/off, and actuators on/off, check to see that the lights on the PLC I/O cards agree. If any of the light disagree with the physical reality, then interface electronics/mechanics need inspection.
4.Consult the manuals, or use software if available. If no obvious problems exist the problem is not simple, and requires a technically skilled approach.
5.If all else fails call the vendor (or the contractor) for help.
32.2.2Forcing
Most PLCs will allow a user to force inputs and outputs. This means that they can be turned on, regardless of the physical inputs and program results. This can be convenient for debugging programs, and, it makes it easy to break and destroy things! When forces are used they can make the program perform erratically. They can also make outputs occur out of sequence. If there is a logic problem, then these don’t help a programmer identify these problems.
Many companies will require extensive paperwork and permissions before forces can be used. I don’t recommend forcing inputs or outputs, except in the most extreme circumstances.
32.3 PROCESS MODELLING
There are many process modeling techniques, but only a few are suited to process control. The ANSI/ISA-S5.1-1984 Piping and Instrumentation Diagram (P&ID) standard
plc software - 32.4
provides good tools for documenting processes. A simple example is shown in Figure 32.1.
FV
11
control valve
Figure 32.1 A Process Model
The symbols used on the diagrams are shown in the figure below XXXXXXXXXXXXX. Note that the modifier used for the instruments can be applied to other discrete devices.
plc software - 32.5
Discrete Device Symbols
Instruments
field mounted
panel mounted
unaccessible or embedded
auxilliary location, operator accessible
Controls
Computer Function
PLC
Shared Display/Control
Figure 32.2 Symbols for Functions and Instruments
The process model is carefully labeled to indicate the function of each of the function on the diagram. Table 2 shows a list of the different instrumentation letter codes. XXXXXXXXXXXXXXXXXXXXX
Table 1: ANSI/ISA-S5.1-1984 Instrumentation Symbols and Identification
LETTER |
FIRST LETTER |
SECOND LETTER |
|
|
|
|
|
|
A |
Analysis |
Alarm |
|
|
|
B |
Burner, Combustion |
User’s Choice |
|
|
|
plc software - 32.6
Table 1: ANSI/ISA-S5.1-1984 Instrumentation Symbols and Identification
LETTER |
FIRST LETTER |
SECOND LETTER |
|
|
|
|
|
|
C |
User’s Choice |
Control |
|
|
|
D |
User’s Choice |
|
|
|
|
E |
Voltage |
Sensor (Primary Element) |
|
|
|
F |
Flow Rate |
|
|
|
|
G |
User’s Choice |
Glass (Sight Tube) |
|
|
|
H |
Hand (Manually Initiated) |
|
|
|
|
I |
Current (Electric) |
Indicate |
|
|
|
J |
Power |
|
|
|
|
K |
Time or Time Schedule |
Control Station |
|
|
|
L |
Level |
Light (pilot) |
|
|
|
M |
User’s Choice |
|
|
|
|
N |
User’s Choice |
User’s Choice |
|
|
|
O |
User’s Choice |
Orifice, Restriction |
|
|
|
P |
Pressure, Vacuum |
Point (Test Connection) |
|
|
|
Q |
Quantity |
|
|
|
|
R |
Radiation |
Record or Print |
|
|
|
S |
Speed or Frequency |
Switch |
|
|
|
T |
Temperature |
Transmit |
|
|
|
U |
Multivariable |
Multifunction |
|
|
|
V |
Vibration, Mechanical Analysis |
Valve, Damper, Louver |
|
|
|
W |
Weight, Force |
Well |
|
|
|
X |
Unclassified |
Unclassified |
|
|
|
Y |
Event, State or Presence |
Relay, Compute |
|
|
|
Z |
Position, Dimension |
Driver, Actuator, Unclassified |
|
|
|
The line symbols also describe the type of flow. Figure 32.3 shows a few of the popular flow lines.
plc software - 32.7
Connection to process
Instrument Supply
Hydraulic
Pneumatic
Capillary Tube
Electric Signal
EM, Sonic, Radioactive
Mechanical Connection
Software Connection
Figure 32.3 Flow Line Symbols and Types
Figure 32.4 shows some of the more popular sensor and actuator symbols.